1. Field of the Invention
This invention relates to a display panel in which a display element is assembled on a printed board, and more particularly to a connection structure in which external terminals of a display element are connected with connection terminals of a printed board.
2. Description of the Related Art
FIG. 7 is a cross-sectional view showing a conventional fluorescent display panel 3 in which a fluorescent display tube is assembled on the printed board 2. The fluorescent display tube 1 generally has a box-like container 4. The container 4 consists of a front substrate 5 and a base substrate confronting each other in parallel, and a frame-like side plate 7 sandwiched between the substrates 5 and 6 and disposed at the outer periphery thereof. These plate members are securely bonded with a glass sealing agent. Conventionally, a side portion of the base substrate 6 protrudes outward from the side plate 7. The side portion of the front substrate 5 confronting the side portion of the base substrate 6 protrudes outward longer than the side portion of the base substrate 6. Eight wiring conductors are arranged on the inner surface of the base substrate 6. Insulating layers 9 are formed on the wiring conductors 8. The anode conductors 10 formed on the insulating layer 9 are connected to the wiring conductors 8 via the conductors formed in the through holes in the insulating layer 9. Fluorescent substance layers 11 are respectively coated on the anode conductors 10. The anode electrodes 12 are formed as a light emitting display portion. Control electrodes 13 are formed over each of the anode electrode 12. Filament cathodes 14 are suspended over the control electrodes 13.
Various electrodes formed on the base substrate 6 are extracted outward from the container 4 via the wiring conductors 8 formed on the base substrate 6. The wiring conductors extend on the inner surface of the base substrate 6 protruded from the container 4 to form first external electrodes 15. Second external terminals 15 confronting the first external electrodes 15 are formed on the inner surface of the side portion of the front substrate 5. The external terminals 15 correspond to plural linear wiring conductors arranged at predetermined intervals while the external terminals 16 correspond to plural linear wiring conductors arranged at predetermined intervals.
Connection terminals 17 are formed on the upper surface of the printed board 2. The connection terminals 17 are formed of wiring conductors which are arranged in the same pitch as that of the external terminals 15 and 16 of the fluorescent display tube 1 and are the same in number as that thereof. The fluorescent display tube 1 is electrically connected to the printed board 2 via two conductive rubber connectors 18 and 19. The conductive rubber connectors 18 and 19, as shown in FIG. 8, have a three layered structure, respectively. Plural conductive fine wires are buried in the intermediate layer of a nearly rectangular silicone rubber at predetermined intervals. In the fine wires 20, one end protrudes from the upper surface of the rectangular silicone rubber while the other end protrudes from the lower surface thereof.
The fluorescent display tube 1 is inserted in the mounting hole 2a formed in the printed board 2. The first conductive rubber connector 10 is sandwiched between the base substrate 6 and the front substrate 5 protruded from the outer surface of the container 4 of the fluorescent display tube 1. The first conductive rubber connector 18 electrically conducts the first external terminal 15 to the second external terminal 16. The second conductive rubber connector 19 is sandwiched between the front substrate 5 and the printed board 2 and is disposed adjacent to the first conductive rubber connector 18. The second conductive rubber connector 19 is thinner than the first conductive rubber connector 18 but has the same structure as that thereof. The second conductive rubber connector 19 electrically conducts the second external terminal 16 to the connection terminal 17 formed on the printed board 2.
However, the conventional fluorescent display panel 3 has the disadvantage in that since the fluorescent display tube 1 protrudes outward from both sides of the printed board 2, the compressing mechanism becomes complicated to establish an electrical connection between the conductive rubber connector 18 and 19 and the fluorescent display tube 1 and the printed board 2. Moreover, there is the problem in that external terminals must be further disposed on the front substrate 6, in addition to the base substrate 6. There is the problem in that since two conductive rubber connectors 18 and 19 establish an electrical connection between the base substrate 6, the front substrate, and the printed board 2 at four spots, conduction failure occurs with high probability.